DESCRIPTION: The major goal of the proposed research is the study of genes whose products are involved in the processes mediating chromosome segregation during meiosis in Drosophila females. Special attention will be paid to the mechanisms underlying chromosome pairing during the first meiotic division. Dr. Hawley's laboratory is currently screening through very large collections of mutations obtained by mobilization of marked P element constructs for lines that affect the segregation of the X and/or 4th chromosomes. They have found to date 28 meiotic mutants, 8 of which have strong phenotypes. These mutants fall into two broad categories: those defective in recombination and those that interfere with the segregation of non-exchange chromosomes. One of the recombination-defective mutants, mei-P22, as well as a previously characterized presumed point mutant (mei-W68) completely abolish recombination. Interestingly, long stretches of synaptonemal complex are observed in the germarium of ovarioles of both of these mutants. This suggests that in Drosophila, pairing and synapsis are independent of, and probably temporally preceed, recombination. These results disagree with findings in yeast, where the initiation of recombination occurs prior to formation of the synaptonemal complex. Thus, fly and yeast meiotic systems may be organized quite differently. Dr. Hawley also intends to investigate another recombination-defective mutant, c(3)G, which blocks synapsis as well as recombination, and thus may define an earlier step in meiosis.